1. Field of the Invention
This invention relates to radiation curable organosiloxane compositions. More particularly, this invention relates to fluorinated organosiloxane compositions that cure upon exposure to ultraviolet radiation to yield gels and elastomers that are resistant to solubilization in liquid hydrocarbon, exhibit improved electrical performance and provide suitable coatings and encapsulants for electronic components.
2. Description of the Related Art
In U.S. Pat. No. 4,719,275, issued on Jan. 12, 1988, Benditt et al. teach fluorosilicone compositions that cure via hydrosilylation reactions. These compositions contain a fluorinated polyorganosiloxane, a fluorine containing organohydrogensiloxane and a platinum catalyst.
In U.S. Pat. No. 5,063,102, issued on Nov. 5, 1991, Lee et al. teach a radiation curable organosiloxane gel comprising a polymethylsiloxane containing (CH.sub.3).sub.2 SiO, CH.sub.3 SiO.sub.1.5, (CH.sub.3).sub.3 SiO.sub.0.5, and other siloxane units; a mercaptoalkyl-substituted polyorganosiloxane; and a photoinitiator.
In U.S. Pat. No. 5,302,627, issued on Apr. 12, 1994, Field et al. teach a method for indicating a cure point for an ultraviolet radiation curing composition comprising the step of adding a dye with a visible color to an ultraviolet curable composition. Field et al. also teach an ultraviolet curable composition comprising a polymethylsiloxane containing (CH.sub.3).sub.2 SiO, CH.sub.3 SiO.sub.1.5, (CH.sub.3).sub.3 SiO.sub.0.5, and other siloxane units; and a mercaptoalkyl- and halohydrocarbon-substituted polyorganosiloxane.
The unique physical and chemical properties of fluorinated organosiloxanes make them desirable as coatings and encapsulants for electrical and electronic devices to protect these devices from moisture, other contaminants and mechanical abuse, all of which can cause the device to malfunction or become inoperative.
Electronic components associated with electronic ignition and emission control systems of automobiles and other vehicles powered by internal combustion engines are often located in the engine compartment of the vehicle where they are exposed to various hydrocarbons including hydrocarbon fuels and lubricating fluids.
The introduction of fluorinated hydrocarbon radicals into a polyorganosiloxane to impart resistance to swelling and/or solubilization by the liquid hydrocarbons present in gasoline and other fuels is disclosed in U.S. Pat. No. 2,979,519, which issued to Pierce et al. on Apr. 11, 1961 and U.S. Pat. No. 3,719,619, which issued to Brown on Apr. 20, 1965.
The present inventors discovered that when compositions comprising an alkenyl-substituted fluorinated polyorganosiloxane; a mercaptoalkyl-substituted fluorinated polyorganosiloxane; and a photoinitiator are exposed to ultraviolet radiation, the compositions cure in a minute or less and that cured gels and elastomers so prepared are resistant to solubilization in liquid hydrocarbons. Moreover, cured gels and elastomers prepared using the compositions of the present invention have unexpectedly improved electrical performance when used in electronic modules.